Call an external API

Prerequisets

Configure a proxy that can call the Slack API with authentication. You can read more about how to configure a custom proxy here
Have a Slack app that can be called and it is added to the channels you are going to use for your notifications.

Actions used

debug:log
https:backstage:request

You can check the available actions if you visit /templates/actions.

Walkthrough

apiVersion: scaffolder.backstage.io/v1beta3
kind: Template
metadata:
  name: send-slack-notification
  title: Send Slack notification
  description: This template demonstrates the https:backstage:request action by calling a configured proxy to send a request towards the Slack API to send a notification to the selected channel
spec:
  owner: group:default/engineering
  type: service

  parameters:
    - title: Send notification to Slack channel
      properties:
        text:
          title: Notification message
          type: string
        channel:
          title: Channel name to send notification
          type: string

  steps:
    - id: log-message
      name: Log Message
      action: debug:log
      input:
        message: Template execution started

    - id: 'send-notification'
      name: 'Send Notification'
      action: 'http:backstage:request'
      input:
        method: 'POST'
        path: 'proxy/slack/chat.postMessage'
        headers:
          content-type: 'application/json; charset=utf-8'
        body:
          channel: ${{ parameters.channel }}
          text: ${{ parameters.text }}

Breakdown

Parameters

This section configures the frontend for your template. Essentially these values will be provided from the Backstage UI to the template.

This renders 2 separate input fields for the template. Both of them are type string means they’ll be presented as an input box on the UI and the user who triggers the action will be able to provide values for it.

parameters:
  - title: Send notification to Slack channel
    properties:
      text:
        title: Notification message
        type: string
      channel:
        title: Channel name to send notification
        type: string

Steps

debug:log

Uses the debug:log action to output a log message to the Backstage scaffolder UI. The message here is a general hard-coded message that indicates that the template execution has started.

- id: log-message
  name: Log Message
  action: debug:log
  input:
    message: Template execution started

http:backstage:request

Uses the http:backstage:request. This action makes an arbitrary HTTP request against the configured Slack proxy.

- id: 'send-notification'
  name: 'Send Notification'
  action: 'http:backstage:request'
  input:
    method: 'POST'
    path: 'proxy/slack/chat.postMessage'
    headers:
      content-type: 'application/json; charset=utf-8'
    body:
      channel: ${{ parameters.channel }}
      text: ${{ parameters.text }}

The input.method required parameter specifies what method you’d like to use. The input.path required parameter is the path that will be called. Here we call the proxy/slack/chat.postMessage because we have a configured proxy which proxies the incoming requests towards the https://slack.com/api URL. The input.headers parameter is the headers that will be provided in the request as the headers. The input.body is the request body. The input.body.channel is the channel ID where you’d like to send your notification message. The input.body.text is going to be the message that will show up in your slack channel.